The invention relates to a semiconductor laser having a semiconductor body comprising a strip-shaped active region situated within a resonator, in which the radiation is emitted in the longitudinal direction of the strip-shaped active region and in which a number of parallel-arranged p-n junctions are present to inject charge carriers into the active region.
A semiconductor laser of the kind described is known from U.S. Pat. No. 3,510,795.
Semiconductor lasers having a strip-shaped active region are frequently used nowadays, usually in the form of lasers having a single or a double hetero junction (DH lasers) as described, for example, in Philips Technical Review, Vol. 36, No. 7, 1976, pp. 190-200. These lasers comprise an active layer which on at least one side adjoins a passive layer having a larger band spacing, in which active layer the radiation is generated.
In these lasers, ageing phenomena occur in the course of their lives, which are expressed inter alia in the increase of the threshold current, that is to say, the minimum current strength at which stimulated radiation emission occurs, and in the occurence of spontaneous oscillations and pulsations, respectively, in the intensity of the emitted radiation.
It has been found that the occurence of such spontaneous oscillations is often associated with the formation, in the strip-shaped active region of the active layer, of regions having locally increased non-radiating recombinations of charge carriers and increased damping resulting therefrom. As a result of the increased nonradiating recombination, a local rise in temperature occurs so that the band spacing is slightly reduced. This in turn again leads to larger damping. These locally occuring regions often prove to be agglomerations of crystal lattice defects which have a tendency to expand, during the life of the laser, over the whole strip-shaped active region so that the laser soon becomes useless. It has been found that lasers having a comparatively very small active volume are less troubled by the occurence of spontaneous oscillations. However, these lasers are often difficult to manufacture.
In the above-mentioned U.S. Pat. No. 3,510,795, a semiconductor laser is described having a strip-shaped active region in which the p-n junction injecting in said region is divided into number of mutually parallel arranged p-n junctions so as to obtain a better cooling.